1. Field of the Invention
This invention relates to unsaturated polyesters which are derived from an acid component of an unsaturated and, in some cases saturated dicarboxylic acid and an alcohol component, particularly a polyvalent alcohol component. More particularly, this invention is directed to thermally stable unsaturated polyesters and to unsaturated polyesters which can be formed into finished articles possessing high thermal stability. More especially this invention is directed to unsaturated polyesters wherein at least a portion of the compounds which are condensed with the compound containing the acid moiety are certain chloroxylylene containing compounds. This invention is particularly addressed to resinous solutions unsaturated polyesters which possess good shelf life.
2. Discussion of Prior Art
Unsaturated polyesters which are derived, as regards the acid component, from unsaturated and, in some cases, saturated dicarboxylic acids or dicarboxylic acid mixtures, and as regards the alcohol component, from polyvalent alcohols, are known. Their molecular weights usually range from about 1000 to 4000.
The unsaturated dicarboxylic acids may be, for example, aliphatic or cycloaliphatic dicarboxylic acids individually or in mixtures. Maleic acid or its anhydride, or fumaric acid, are used preferentially.
The saturated dicarboxylic acids may be, for example, aliphatic or cycloaliphatic or aromatic dicarboxylic acids individually or in mixtures. Preferred are orthophthalic acid or its anhydride and/or isophthalic acid and/or terephthalic acid or dimethylterephthalate and/or tetrahydrophthalic acid and/or adipic acid and/or hexachlorendomethylenetetrahydrophthalic acid.
The polyvalent alcohols are mainly ethylene glycol, propanediol-1,2 and neopentylglycol, mixed, if desired, with lesser amounts of a more than bivalent alcohol, such as trimethylolpropane for example. The unsaturated polyester resins (hereinafter called UP resins) are used in the form of their solutions in a polymerizable monomer, preferably styrene, mainly as casting resins for the production of a wide variety of moldings, an example being the bonding of glass fiber mats or the like. After the addition of radical formers, the UP resin solution, containing a filler if desired, is hardened after shaping, and in some cases post-hardened. Since even at room temperature crosslinking occurs, although slowly, the radical former is not added to the UP resin solution until shortly before it is used. Examples of the radical formers are peroxides, preferably dibenzoylperoxide alone, in the form of a 50% paste, for example, or mixed with tertiary amines such as dimethylaniline.
A very important requirement for the practical application of UP resin solutions is the shelf life of the solutions. In the period between the preparation and the application of the solutions, which may amount to weeks or even months, no alteration of the UP resin solution must occur which would diminish its usefulness. Such undesirable alteration would be, for example, the gel-like stiffening of a UP resin solution during storage at room temperature.
If a UP resin is prepared on the basis of neopentylglycol (100 mole-%) and dimethylterephthalate (26 to 40 mole-%, with reference to the dicarboxylic acid component), isophthalic acid (0 to 14 mole-%) and fumaric acid (60 mole-%) and is dissolved in a proportion of 60 weight parts in 40 weight parts of styrene, it will undergo a gel-like stiffening in 24 to 48 hours at room temperature. The gelling, however, is not due to an incipient cross-linking copolymerization of the resin with the monomer; instead, it is a thixotropic phenomenon that is involved. Despite the fact that the mechanical characteristics of the hardened UP resins are good, especially their Martens thermal stability of shape, of 120.degree. to 125.degree. C., and their thermal stability of shape in accordance with ISO/R 75, A, of 136.degree. to 140.degree. C., the thixotropy of the styrene solution of the UP resin of the above composition makes it entirely unsuitable for use as a casting resin. The shelf life of the styrene solution of the UP resin can be improved by using as the diol component a mixture of at least 25 mole-% ethylene glycol or propanediol-1,2 and no more than 75 mole-% neopentyl glycol. The shelf life which is thereby attained, however, is achieved at the cost of a considerable loss of 10.degree. to 15.degree. C. in the thermal stability of shape of the castings according to the Martens or ISO/R 75 A standards, and of a lowered resistance to hydrolysis.
It has therefore become desirable to provide a solution of unsaturated polyester, particularly a solution thereof in a copolymerizable monomer which possesses good shelf life, does not form a thixotropic solution and provides castings or molded articles having high thermal stability and good resistance to hydrolysis. It is therefore an object of the invention to provide an improved unsaturated polyester which when included in such solution of copolymerizable monomer does not form a thixotropic composition or following copolymerization and setting of the material, form a material which has poor thermal stability.